This application is a based on our previously funded 5-year project that generated over 40 peer-reviewed publications. Invasion-promoting, pro-tumorigenic MT1-MMP is implicated as the most important MMP in cancer biology and is known to play specialized roles as a modifier of cell function. There is a consensus among scientists that MT1-MMP is a key player in cell surface proteolytic events. We now know that in multiple model systems MT1-MMP acts as an oncogene, stimulates tumor cell invasion and metastasis, and takes over tumor growth control. In agreement, in humans MT1-MMP activity correlates significantly with metastases, clinical stage, and tumor size. Our knowledge of the MT1-MMP biology, however, is limited as yet especially when compared with the role this proteinase plays in malignancy. As of now, the mechanisms of MT1-MMP activation are not completely understood. As a result of our study we can now suggest that rather than exhibiting a uniform activation pathway in any cell type, invasion-promoting MT1-MMP appears to have an activation mechanism hierarchy. To increase their proteolytic arsenal, tumor cells exploit the mechanism leading to the complete inactivation of the MT1-MMP's autoinhibitory prodomain while in normal cells MT1- MMP activity is controlled by the intact prodomain that is released by furin cleavage alone. As a result, the intact prodomain prevents the potentially damaging function of pro-invasive, pro-tumorigenic MT1-MMP in the normal microenvironment. Autocatalytically activated furin plays an important role in the processing and activation of multiple proproteins including MT1-MMP and MMP-2, the downstream target of MT1-MMP. Because of its importance in cancer, MT1-MMP is a promising drug target in disease and its selective biosensor and inhibitors are urgently needed. Overall, it is obvious that additional work is needed to gain a better understanding of the MT1-MMP structural-functional relationships. Our three Specific Aims, which we have designed to achieve a better understanding of MT1-MMP are: (1) Determine the functional significance of a two-step prodomain processing mechanism of MT1-MMP activation in normal and cancer cells, (2) Design and test efficient and selective, cleavage-activated biosensors of MT1-MMP and furin (an activator of MT1-MMP), and (3) Design and evaluate the anti-tumor activity of the highly selective and potent, active site- targeting, inhibitory Fab/scFv human antibodies to MT1-MMP. The result of our proposed studies will be a thorough understanding of the many roles played by MT1-MMP and its activator, furin. Our program will use an integrated systems approach involving biochemical, molecular, cellular and computer modeling studies. We will also conduct studies using tumor xenografts in mice to validate our results gained in vitro. Our program will result in a refined understanding of how malignant cells traffic from their original location and spread throughout the body. This valuable information will lead directly to the development of novel and effective strategies for the detection, prognosis, and treatment of a broad range of malignancies.